Printable display devices have attracted a lot of attention, and a lot of global research efforts have been carried out during the recent years. Regardless of the display performance; short or long life time, high or low resolution, short or long switching time etc., the most critical issue in order to obtain high yield at low production cost has been to establish the most simple manufacturing process by involving as few materials and processing steps as possible. Manufacturing of display devices, which sometimes consist of both pixels and addressing transistors, often requires material patterning at high accuracy on top of a flexible substrate. Such material patterning can, for example, consist of the deposition of the insulating, semiconducting and conducting materials serving as the dielectric, active and electrode materials, respectively, of a display device. One of the major objectives in order to enable manufacturing at low cost and high volume is to combine flexible polymer materials with roll-to-roll printing and/or coating equipments. Therefore, the capability of rapid and simple patterning of deposited materials at high yield is one of the most critical issues that need to be addressed within the field of printed electronics.
One example of a process for manufacturing electrochromic display devices comprising electrolyte is described in Andersson P. et al: “Printable All-Organic Electrochromic Active-Matrix Displays”, Advanced Functional Materials, vol. 17, no. 16, 5 Nov. 2007, pages 3074-3082. The article describes, in section 4 Experimental, the manufacturing of an electrochromic device comprising electrolyte, wherein transistor and pixel electrodes are formed on two PEDOT:PSS-covered sheets by means of subtractive patterning, i.e. predetermined portions of the PEDOT:PSS layer are removed such that the desired PEDOT:PSS electrodes are formed. Two masks are made by cutting openings in a plastic foil. When ready, each mask is arranged on a respective one of the PEDOT:PSS-covered sheets, and the mask openings are filled with electrolyte using e.g. a screen printer squeegee. Hence, the electrolyte is arranged in ionic contact with each PEDOT:PSS layer. Finally, the two sheets are laminated together, such that ionic contact is provided between a display electrode and/or a transistor channel on the first sheet and a display counter electrode and/or a transistor gate electrode on the other sheet via the electrolyte, as is illustrated in FIG. 4a in the article.
Although good results may be achieved by the above manufacturing process there is a desire to enhance the pixel resolution and preferably also to reduce the manufacturing time. However, the plastic foil limits the pixel to pixel distance. If the pixels are made substantially smaller (e.g. in the order of 1 mm2) and arranged substantially closer to each other (e.g. having a pixel to pixel distance in the order of less than 500 μm, the stability of the foil will be severely impaired due to lack of stabilizing material.
In US 20060116001, from the remote technical field of pixels devoid of electrolyte material, there is described a method wherein a stamp is arranged in contact with a substrate for a substantial amount of time (according to the example given: two days), which stamp modifies the surface energy of a substrate such that when the substrate is later dip-coated in a conjugated polymer solution, the conjugated polymer wets and spreads only on the area with higher surface energy. However, this technique is not relevant for achieving the objects of the invention, e.g. to that there is no guidance in the document as how this technique, relating to devices having a layer of semiconducting or a light emitting material applied to polymer, may be modified so as to be applicable to the manufacturing of a display comprising layers of electrolyte sandwiched between pairs of two electrodes/display elements; and also due to the substantial amount of time the stamp needs to be in contact with the substrate—the demands for high yield and short manufacturing time do not normally allow for a manufacturing step which takes days to complete. Furthermore, the requirement of a pre-patterned material layer implies an additional processing step during the display device manufacturing, which in turn increases the risk of registration errors.